A manufacturing method of an all-solid battery includes fabricating a single battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer arranged between the positive electrode layer and the negative electrode layer; fabricating a plurality of battery packs including the plurality of single batteries; confining a plurality of battery packs by an equal confining pressure; measuring the electrical characteristics of the plurality of confined battery packs; determining the battery pack whose measured electrical characteristics are the worst of the plurality of battery packs; reducing the confining pressures of the other battery packs so that the electrical characteristics of the other battery packs are equal to that of the battery pack whose electrical characteristics have been determined to be the worst; and electrically connecting in parallel the battery packs.